(1) Field of the Invention
The present invention relates to a television channel selection monitoring apparatus for detecting the television channel to which the television receiver equipment was tuned at any given time and, more particularly, to a monitoring apparatus of this type adapted to identify a television channel selected out of those broadcast through a communication satellite in digital form (CS digital broadcast), through a CATV network or through a conventional ground wave broadcast system.
(2) Description of the Related Art
In the broadcast industry, the so-called ratings indicative of audience size for each of the programmings are important, particularly for determining advertising rates and for adjusting programming. To calculate the ratings, the viewing habits of sample households must be monitored non-obtrusively without disturbing such habits.
For that purpose, an apparatus called television (TV) sensor is conventionally connected to each of the monitored objects such as television sets or video tape recorders installed at sample households, so that data as to the television channels viewed and the times of viewing for each of those monitored objects may be obtained and that such data may be supplied to a central computer through telephone lines periodically.
One example of such TV sensor to be placed at sample households, which is disclosed in the Japanese Patent Application Kokai Publication No. H4-4626, is adapted to pick up local oscillation frequency of the tuner of the monitored equipment to permit the detection of the channel, to which the monitored equipment is tuned to. This is based on the fact that such channel and local oscillation frequency are in one to one correspondence to each other.
While such prior art channel detection techniques based on the local oscillation detection at tuner have been usable for the detection of television channels of ordinary broadcast system based on analog signal transmission such as the existing ground wave broadcast system or the FM-based satellite analog broadcast system, they are not applicable to CS digital broadcast. It is because the CS digital broadcast employs the digitization and data compression of video and/or audio signals to achieve the multiplexed transmission of four to eight television channels through a single satellite transponder, which makes it impossible to use the conventional tuner local oscillation frequency-based identification of channels to which the receiving equipment is tuned.